Organic chemistry performed at the solid-liquid interface allowed us to achieve the selective chain-end functionalization of poly(ethylene terephthalate) (PET) membranes and films with perfluorinated labels. The carboxyl endings were activated with water-soluble carbodiimide and were coupled to 3,5-bis(trifluoromethyl)benzylamine (1) in aqueous acetonitrile, whereas the hydroxyl endings were activated by tosylation and were also coupled to 1. 3,5-Bis(trifluoromethyl)phenyl isocyanate (2) was directly fixed on the hydroxyl endings of the polymer substrates in dry organic media. All the derivatized materials were analyzed by X-ray photoelectron spectroscopy, allowing the quantitative determination of the amounts of surface-grafted labels. Yields were between 10 and 100 pmol/cm(2). These surface reactivity assays mimic at best the experimental conditions that would be applied for the covalent anchorage of biologically active molecules onto PET substrates used in cell culture systems.